Printing apparatuses, such as printers and fax machines that print onto roll paper are conventionally known. Compared to apparatuses that print onto cut sheets, such printing apparatuses require less space for storing printing paper and so can be produced in more compact overall sizes. However, the curling tendency of roll paper causes problems when printing on roll paper. The curling tendency remains for roll paper that has been printed upon and outputted from a printing apparatus, so that such paper curls after output. This means that even if the printed paper is cut into a predetermined size, such as Japanese A4 size, when it is outputted from a printer, it is not possible to store the printed paper in a stack in a paper stocker or the like. Since the outputted paper sheets are curled, it is more difficult to gather a plurality of sheets together in a bundle and file the sheets. Accordingly, printing paper in the form of sheets or pre-cut sheets are preferred at present for printing, and printers and fax machines are made large in order to store printing paper in the form of sheets.
The increasingly widespread use of mobile terminals such as PDAs and mobile telephones has been accompanied with strong demands for compact printers that can be used together with such devices even if the user is out of office. While printers that use roll paper as the printing paper are suited to being made compact, for such printers to be easy to use, it is important to correct, remove or straighten the curling tendency (the curl) of the roll paper using a compact mechanism. In particular, since a compact printing apparatus for a mobile terminal such as a PDA will need to use roll paper with a diameter of around 10 mm or less, the printed paper (“print out”) outputted will be sure to curl and ends up curling up with a diameter of 10 mm or less. Compared to print outs that have curled up with a large diameter, print outs that have curled up with a small diameter are much more difficult to handle, so that it becomes very important to correct the curling tendency.
A mechanism in which roll paper is pressed by a paper guide with a sharp-angled tip using a spring or other force can conceivably be used as a mechanism for removing the curl of roll paper. However, since setting the paper guide with the sharp-angled tip on the paper pass makes the paper route being changed, and a space for the spring for pressing the paper guide onto the paper is necessary, a large space is occupied by the mechanism for correcting the curl. Accordingly, it is not possible to realize a compact printer. Also, the curl-correcting performance is not especially high, so that there is the fundamental problem that the method of the above is essentially not effective for roll paper with a small diameter.
Also, since the roll paper is additionally held by the paper guide and the spring on the paper pass, there is increased resistance for paper feeding, which makes it necessary to use a motor with an output that can handle this load. Accordingly, the size of the motor increases and power consumption also increases, which makes this technology even less suited to the realization of a compact printer.
In addition, since the roll paper is held by the paper guide with the sharp-angled tip and the spring on the paper pass, when the printer is a standby mode, the roll paper is continuously held by the sharp-angled tip, so the held part becomes curled in the opposite direction. Accordingly, print-outs become a paper curled as a whole in the same direction as the roll paper but have tips that curl in the opposite direction, such print-outs are extremely difficult to handle and also have a poor appearance. It is possible to prevent curling in the opposite direction through methods such as moving the spring away when the printer is in standby mode, though enclosing a mechanism for doing so further increases the size of a printer and also increases the cost.
For this reason, it is an object of the present invention to provide a paper feeding apparatus that is compact and is capable of correcting the curling tendency of roll paper and also a printing apparatus equipped with such paper feeding apparatus. It is a further object to provide a paper feeding apparatus that can suppress increases in the load of a motor and does not impart a tendency in. the opposite direction, and also a printing apparatus equipped with such paper feeding apparatus. It is yet another object to provide a printing apparatus that uses roll paper as the printing paper, is easy to use, and is extremely compact so as to be well suited to being carried together with a mobile terminal such as a mobile phone.